DE4426443A1 - Improved process for the production of polycarboxylates by oxidation of polysaccharides - Google Patents

Abstract

The invention concerns a process for preparing polycarboxylic acids or their salts from polysaccharides by oxidization with gaseous nitrogen dioxide/dinitrogen tetroxide by converting at least some of the primary alcohol groups of the polysaccharides into carboxyl groups and optionally neutralizing the resultant carboxylic acid groups at least proportionally. This process substantially simplifies the requisite preparation in that the delivery of nitrogen dioxide/dinitrogen tetroxide is terminated when at most 90 % of the necessary degree of conversion of the primary alcohol groups into carboxyl groups has been reached, and the temperature is increased by at least 10 DEG C. The resultant polycarboxylates are used, for example, as builders or co-builders in detergents and cleaning agents.

Description

The invention relates to a simplified method for producing Polycarboxylates by selective oxidation of polysaccharides with gas shaped nitrogen dioxide.

For the production of polycarboxylates by oxidative treatment of poly saccharides, such as cellulose, starch and dextrins, consists of extensive knowledge. Reference is made, for example, to Houben-Weyl "Metho that of organic chemistry ", Thieme-Verlag, Stuttgart (1987) Vol. E 20, Macromolecular substances, here the subsection "Polysaccharide derivatives" works by Dr. K. Engelskirchen, op. Cit. Page 2042 ff, especially Sei te 2124 ff (oxidation products of cellulose) and page 2166 ff (oxidized Strengthen). Please also refer to the publication "Cellulose Chemi stry and Its Applications "(1983), John Wiley & Sons, Chichester, UK in particular T. P. Nevell, "Oxidation of Cellulosea" (Chapter 10) and the extensive literature cited there, loc. cit. pages 262 to 265.

In a nutshell: A large number of oxidizing agents are for the Oxidation of polysaccharides, especially from glucose only constructed polyglucosans in use. For example (Air) oxygen, hydrogen peroxide, sodium hypochlorite respectively -bromite, periodic acid or periodate, lead (IV) acetate, stick Substance dioxide and cerium (IV) salts. These oxidants react very un different from the anhydroglucose units, cf. for example the Formula pictures in Houben-Weyl op. Cit. Page 2124. For example Periodates or lead (IV) acetate a C-C cleavage of the anhydroglucose rings; the so-called 2,3-dialdehyde cellulose and analog are obtained from cellulose from starch dialdehyde starch. It is also known that the action  from nitrogen dioxide to cellulose the oxidation of primary alcohol group to the carboxyl group is the predominant reaction. The Oxida agent, usually in equilibrium with nitrous oxide lying, can be gaseous or dissolved in an inert organic Solvents are used, cf. Houben-Weyl op. page 2125 and the primary literature mentioned there in this context. Also based on the strength can be largely selective accordingly Oxidations of the primary alcohol group of the anhydroglucose units Create carboxyl group.

So is from the US patent US 2 472 590 the oxidation of starch with gaseous or in Water or in various organic solvents dissolved nitrogen dioxide at room temperature and normal pressure.

Under these conditions, the conversion is almost complete the primary alcohol groups of the polysaccharides in carboxyl groups after very long reaction times, which may be up to several days conditions. In addition, the known methods are high Amounts of nitrogen dioxide, based on the polysaccharide to be oxidized, are required does.

From the international patent application WO 93/16110 is an essential one Improve the production of such oxidation products of polysaccha known. The invention disclosed there is based on the knowledge that that polycarboxylates from polysaccharides in a simple process in high yields can be obtained if the oxidation reaction with stick Substance dioxide / nitrous oxide in the presence of oxygen at elevated Temperatures and preferably at elevated pressures. The The phrase "nitrogen dioxide / nitrous oxide" stands here as well in the present invention, for that under the respective reaction conditions existing equilibrium mixture of nitrogen dioxide and be a dimer of dinitrogen tetroxide.

Especially when you consider the variant of the Suspension- and solvent-free oxidation with gaseous nitrogen carried out dioxide / nitrous oxide, it was observed that in Rah  Men working up the oxidation product on the there in all the annexes play listed step of washing with water to make the nitrate be or the nitrite content of the oxidation product to be as low as possible Lowering values is hard to do without if you don't the vacuum degassing also mentioned there over a long period of time wants to perform. Both process variants have their disadvantages: The non-aqueous work-up with the help of vacuum treatment required under Perhaps a period of several hours to days, and the watery In addition to the occurrence of contaminated wastewater, processing makes it dry step of the cleaned product is unavoidable if it is not in aqueous liquid to pasty agents to be used.

Surprisingly, it has now been found that both on the aqueous Aufar processing of the reaction products of polysaccharides with nitrogen di oxide / nitrous oxide as well as their vacuum treatment can become and still products with acceptably low nitrate and nitrite levels, if you get the actual oxide before completion reaction the supply of the oxidizing agent nitrogen dioxide / Distick substance tetroxide terminated and the temperature to a value above the Re action temperature increased.

The invention accordingly relates to a process for the production of polycarboxylic acids or their salts from polysaccharides by oxidation with gaseous nitrogen dioxide / nitrous oxide at one temperature in the range of 30 ° C to 150 ° C with conversion of at least part of the primary alcohol groups of the polysaccharides in carboxyl groups and against if necessary, at least partial neutralization of the resulting car bonic acid groups, which is characterized in that the supply of nitrogen dioxide / dinitrogen tetroxide terminated when desired Degree of conversion of the primary alcohol groups to carboxyl groups to high at least 90% is reached, and the temperature is increased by at least 10 ° C.

This degree of conversion can be easily determined by determining the Acid number of the oxidation product, such as in the international Nalen patent application WO 93/16110 described can be determined.

Otherwise the oxidation can be carried out as in the international Patent application WO 93/16110 described, as long as care is taken that the reaction carried out there until the end is only carried out for so long that the desired degree of oxidation, that is, the degree of conversion of the primary Alcohol groups in carboxyl groups, only to a maximum of 90%, preferably to 60% to 85% and in particular 65% to 80% is achieved. The full constant achievement of the desired degree of oxidation occurs fiction only in the post-oxidation phase, i.e. when nitrogen has ended dioxide / nitrous oxide supply and compared to the oxidation phase at least 10 ° C, preferably 15 ° C to 80 ° C and in particular 20 ° C to 50 ° C elevated temperature. It is important to ensure that the Er If possible, the temperature should not exceed an upper limit of 160 ° C step, since decomposition is increasingly observed at higher temperatures was done.

Another advantage of the method according to the invention is that one does not refer to the particularly preferred implementation of WO 93/16110 Reaction at elevated pressures of up to 10 bar, for example but the reaction is practically depressurized, i.e. at normal pressure, can lead. The method according to the invention is preferably used in a Pressure in the range from 0.8 bar to 9 bar, in particular from 1 bar to 3 bar carried out.

A polycarboxylate produced by the process according to the invention sits as a further advantage of the invention, a much lower exo Therm-energetic potential as products in which the Invention according to the characteristic method step was not carried out. This works favorably on its storability.

The one to be canceled according to the invention before full conversion is reached Oxidation reaction is preferably carried out at temperatures from 30 ° C to 70 ° C, performed in particular from 40 ° C to 60 ° C. Oxygen, al alone or in a mixture with gas which is inert under the reaction conditions be essential, its addition once at the start of the reaction or several times, if desired, continuously during the reaction. At as is known, the latter reaction can be carried out by the oxidation reaction  Controlled via oxygen metering depending on temperature or pressure will. The addition of oxygen is preferably controlled so that the reacti on temperature remains in the range of 30 ° C to 70 ° C.

As inert, that is, under the desired process conditions non-reactive gases can be noble gases such as helium or argon and coal dioxide, but especially nitrogen, nitrogen monoxide and nitrous oxide monoxide, but also any mixtures of such gases can be used. The oxygen content in the gas mixture is preferably in the loading ranges from 1% by volume to 30% by volume, in particular from 3% by volume to 10% by volume. A preferred embodiment of the method according to the invention includes the supply of oxygen by injecting air.

A further preferred embodiment of the method is thereby ge indicates that in the reaction system before the start of the oxidation reaction Pressure of less than 10 bar, in particular from 2 bar to 6 bar, at the Desired reaction temperature by pressing an inert gas mentioned It is set and then oxygen or a mixture of Oxygen with said inert gas, several times, if desired, con instantly, is pressed. The addition of nitrogen dioxide / Distick Substance tetroxide can relate before or after the addition of oxygen as the beginning of the oxygen addition. It may be necessary be the reaction vessel after the initial injection of the inert gas to heat to the desired reaction temperature. During the process the oxidation reaction, which is expedient with intensive mixing of the Reaction partner takes place, the reaction temperature can usually without external heating is held solely by the addition of oxygen the.

In the method according to the invention, the oxidizing agent comes out of the Gas phase directly on the solid, thoroughly mixed substrates for action. Oxidation in a fluidized bed is preferred Made of polysaccharide, the fluidizing agent of which is a gas containing nitrogen dioxide is.

Such an oxidation process is in the unpublished German patent application P 44 02 851.2 described. Under fluidized bed should - without being limited to this type of production - the  Appearance to be understood that can be observed when on horizontal fine-grained bulk goods stored in perforated floors from below Gases, referred to as eddies, is flowed through. In this together hang on the work of D. Kunii and O. Levenspiel, "Fluidization Engi neering ". Verlag Butterworth-Heinemann, 2nd edition 1991, there in particular the table on pages 8 and 9 and chapter 3. On usable reactor for the inventive method is also in European patent EP 051 147 B1 (there Fig. 1) disclosed device, where there is a fluidized bed through which gas flows in a cylinder, in which a shaft equipped with stirring arms rotates. It is also possible Use of a reactor with a multi-stage fluidized bed, as in Beranek / Ro se / Winterstein, "Fundamentals of Fluid Bed Technology", Krauskopf-Verlag, 1975, page 72. With such a device, the conti easy reaction management possible.

In this process variant, the fluidizing agent can flow through the Polysaccharides leave the reaction system and will according to the invention The desired degree of oxidation is replaced by a fluidizing agent, that does not contain nitrogen dioxide / nitrous oxide. Is preferred this vortex is an inert gas described above.

If the fluidizing agent containing nitrogen dioxide after flowing through the Po lysaccharide, however, with reoxidation of the spent nitrogen dioxide, for example, by passing the fluidizing agent through a particulate solid, adsorbed onto a solid support material or in liquid dissolved oxygen-transferring oxidant conducts in a circle care must be taken to ensure that this reoxidation is terminated is before the desired degree of oxidation of the polysaccharide is reached.

In the fluidized bed variant of the oxidation process, the required reaction time until the addition of nitrogen dioxide / di nitrogen tetroxide for a given polysaccharide and nitrogen dioxide content in the fluidizing agent essentially from the desired degree of oxidation and Temperature. The following information can serve as a guide: Temperature of 50 ° C and normal pressure using 12 mol equivalents Nitrogen dioxide per hour, based on hydroxyl groups to be oxidized,  become 30% to 22% after 30 minutes, 60% to 70% after 60 minutes and after 1.5 hours 85% to 95% of the primary alcohol groups in carboxyl groups converted.

The nature of the poly used for the process according to the invention is saccharids largely uncritical. The only requirements are that it contains carbohydrate units containing primary alcohol groups and in a form is present, which the intensive mixing with the gaseous against oxidizing agents and preferably the formation of a fluidized bed allows, especially in powder form. Native polyglucans are suitable, in particular starch and / or cellulose, but also other polysaccharides, for example polygalactomannans such as guaran and carubin. The polysaccharides can also be used in chemically or physically modified form if they still contain oxidizable primary alcohol groups. We against the particularly smooth reaction and economy economic reasons are strengths of different provenance, in particular potato starch, wheat starch, corn starch and / or tapioca starch, such as they are commercially available as conventional powders. Because cellulose because of its Fibrousness often causes problems in the formation of a fluidized bed, it is preferably used in the form of micropowder.

The method according to the invention is in particular using the ge called polyglucans preferably performed over such a period that the oxidation product from the statistical average to at least 15 mol% oxidized anhydroglucose units of formula I.

exists, which ent a carboxyl group content of at least 4 wt .-% ent speaks.

A process according to the invention gives polycarboxylates on poly glucan base, which the oxidized anhydroglucose units in particular  of formula I preferably at least 25 mol%, in particular too little contain at least 35 mol% in the molecule, with another advantage being no we substantial quantities of other oxidation secondary products are present. The waiter limit of the content of units according to formula I is 100 mol%, ins especially around 95 mol%. Are preferred by the invention Process polycarboxylates prepared which units according to formula I in Range from 70 mol% to 100 mol%, corresponding to a carboxyl group amount hold up to about 25 wt .-%.

In the event that the polysaccharide to be oxidized for agglomeration and in the fluidized bed technology tends to form dreaded canals hold by adding small amounts of solid additives in particular, to which, for example, magnesium oxide, calcium fluoride, calcium phosphate, finely divided zeolites or silica gel, especially that under the name Aerosil® distributed silicon dioxide belong to those who are significantly improved the. In this regard, high effects are already lower when used Amounts of additives of preferably 0.1% by weight to 5% by weight, in particular 0.25% by weight to 1% by weight, based in each case on the polysaccha to be oxidized rid, reached. The polysaccharide used preferably does not contain more than 15% by weight, in particular not more than 10% by weight, of water.

To illustrate the method according to the invention, reference is made to FIG. 1. This shows a tubular reactor ( 1 ) with temperature sensor ( 2 ), which can be kept at the desired temperature with the aid of a thermostat ( 3 ), and in which the polysaccharide to be oxidized is flowed through by nitrogen dioxide from a storage container ( 4 ) and inert gas N₂ , the gas flows being regulated by valves ( 7 , 8 and 9 ). After leaving the reactor, the gas is preferably passed through a dust separator ( 5 ) and, after passing through a condenser ( 6 ), in which condensable components, in particular water and nitrogen oxides, are separated, leaves the apparatus.

Following the oxidation and post-oxidation reaction, it is possible to at least part of the carboxyl groups of the oxidation product by Be neutralize trade with a basic reagent, that is, from the To convert acid to salt form. As a neutralizing agent  preferably an aqueous solution, the alkali hydroxide, ammonium hydroxide and / or contains organic base used. Also right after the oxidation reaction, neutralization is possible, for example by gassing the reaction vessel with ammonia. The salt formation is too under reducing conditions, for example using Na triumborohydride, possible. The neutralizing agent is preferably in such amounts used that all carboxyl groups of the oxidation product into the salt form. Both the addition of the Oxidation product to the neutralizing agent as well as the addition of the new Tralisationsmittel to the oxidation product possible. Salt formation can also under the conditions of application or further processing tion of the polycarboxylates in their acid form, for example the manufacture or use of detergents or cleaning agents usual alkaline components of such agents.

The polycarboxylates produced by the process according to the invention contain extremely low nitrate and nitrite levels, usually below 3 wt .-% and are preferably used as a builder or co-builder in washing or cleaning agents are used. In such means, they will preferably as a co-builder in amounts of 0.5% by weight to 10% by weight, in particular the other 2 wt .-% to 7 wt .-%, each based on the total weight of the co agents containing inorganic builders as the main builder.

They are particularly preferably used in the latter agents, which Zeolite NaA, such as that used in connection with textile detergents is described in the German patent specification DE 24 12 837, and / or Layered silicates as described in European patent application EP 164 514 are described as the main builder and by the inventive method ren produced polycarboxylic acids or their salts in proportions from 2: 1 to 5: 1 included. The composition of the washing and / or Cleaning agents can otherwise be practical in the context of known recipes can be chosen arbitrarily.

Examples example 1

Starch was oxidized in the apparatus shown in FIG . For this purpose, 1042.8 g of potato starch, moisture content 6.8% by weight, were mixed with 0.5% by weight of Aerosil® 200 and filled into the reactor ( 1 ) (height 80 cm, inside diameter 90 mm). Nitrogen at a rate sufficient to fluidize the starch was passed through the reactor ( 1 ) and heated to 50 ° C. via a thermostat ( 3 ). Nitrogen dioxide was passed through the fluidized bed from a temperature-controlled storage bottle ( 4 ). The quantities of gas were adjusted to 150 standard liters per hour with the aid of flow meters calibrated for air. After 3 hours, the supply of nitrogen dioxide was stopped and a sample (V1) of the product was removed. The reactor temperature was raised to 80 ° C. within 30 minutes and held at this temperature for 30 minutes. The mixture was then cooled to room temperature. A polycarboxylic acid P1 was obtained as a white, free-flowing powder with the data given in Table 1. For comparison, corresponding values of the non-post-oxidized polycarboxylate V1 are also given. The clearly lower nitrite and nitrate content of the product produced by the process according to the invention can be seen.

Example 2

Analogously to Example 1, a polycarboxylic acid P2 (sample V2) was obtained, where however, the reaction time was 4 hours until the reheating phase. The data of the products are also shown in Table 1. You can also see here the significantly lower nitrite and nitrate content of the invention Product P2 manufactured according to the process compared to V2.

Example 3

For comparison, Example 2 was repeated in such a way that the Tem temperature did not increase after the end of the supply of nitrogen dioxide,  but left at approx. 50 ° C. A polycarboxylate V3 was obtained with the data also given in Table 1.

Table 1

Data of the polycarboxylates

Reference list

1 reactor
2 temperature sensors
3 thermostat
4 nitrogen dioxide storage tanks
5 dust separators
6 capacitor
7 , 8 , 9 adjustable valves.

Claims (13)

1. Process for the preparation of polycarboxylic acids or their salts from polysaccharides by oxidation with gaseous nitrogen dioxide / nitrogen nitrogen tetroxide at a temperature in the range from 30 ° C. to 150 ° C. with conversion of at least part of the primary alcohol groups of the polysaccharides into carboxyl groups and optionally at least partially Neutralization of the resulting carboxylic acid groups, characterized in that the supply of nitrogen dioxide / dinitrogen tetroxide is terminated when the desired degree of conversion of the primary alcohol groups into carboxyl groups is at most 90%, and the temperature is increased by at least 10 ° C. 2. The method according to claim 1, characterized in that the supply of nitrogen dioxide / dinitrogen tetroxide terminated when desired Degree of oxidation to 60% to 85%, in particular 65% to 80% is enough. 3. The method according to claim 1 or 2, characterized in that the Temperature increased by 15 ° C to 80 ° C, in particular by 20 ° C to 50 ° C. 4. The method according to any one of claims 1 to 3, characterized in that the oxidation reaction at a temperature in the range of 30 ° C to 70 ° C, in particular 40 ° C to 60 ° C. 5. The method according to any one of claims 1 to 4, characterized in that you have at least 15%, especially 25% to 100% of the primary Alcohol groups of the polysaccharides converted into carboxyl groups. 6. The method according to any one of claims 1 to 5, characterized in that one oxidation in a fluidized bed, the fluidizing agent Gas containing nitrogen dioxide is carried out. 7. The method according to claim 6, characterized in that the vortex medium leads in a circle.   8. The method according to claim 6 or 7, characterized in that one Reoxidation of the nitrogen dioxide in a second reaction zone of the Circulatory system or "in-situ" by adding a gaseous, oxygen-carrying oxidizing agent to the vortex. 9. The method according to any one of claims 1 to 8, characterized in that it, especially at a pressure in the range of 0.8 bar to 9 bar special from 1 bar to 3 bar. 10. The method according to any one of claims 1 to 9, characterized in that as starch to be oxidized, especially Kar potato starch, wheat starch, corn starch and / or tapioca starch puts. 11. The method according to any one of claims 1 to 10, characterized in that it is carried out over such a period that the Oxidationspro product on average at least 15 mol% of oxidized anhydroglucose units of formula I. consists. 12. The method according to claim 11, characterized in that oxidized to hydroglucose units of formula I preferably at least 25 mol%, in particular at least 35 mol% in the molecule are. 13. Use of the manufactured according to a method of claims 1 to 12 ten polycarboxylates as builders or co-builders in washing or cleaning agents.